c = 2.99792458e10           # cm s^-1
h = 6.6260755e-27           # erg s
hbar = 1.05457266e-27       # erg s
G = 6.67259e-8              # cm^3 g^-1 s^-2
e = 4.8032068e-10           # esu
m_e = 9.1093897e-28         # g
m_p = 1.6726231e-24         # g
m_n = 1.6749286e-24         # g
m_H = 1.6733e-24            # g
amu = 1.6605402e-24         # g
N_A = 6.0221367e23          #
k = 1.380658e-16            # erg K^-1
eV = 1.6021772e-12          # erg
a = 7.5646e-15              # erg cm^-3 K^-4
sigma = 5.67051e-5          # erg cm^-2 K^-4 s^-1
alpha = 7.29735308e-3       # 
R = 2.1798741e-11           # erg
